1. Field of the Invention
The invention relates to a fastening structure of a fuel delivery pipe and a cylinder head of an internal combustion engine.
2. Description of Related Art
A fuel delivery pipe that is provided with a plurality of injection nozzles in a cylinder head of an internal combustion engine, and that supplies fuel such as gasoline to a plurality of cylinders is known (see Japanese Patent Application Publication No. 2007-255361 (JP 2007-255361 A) (pp. 5 to 6 and FIG. 1), and Japanese Patent Application Publication No. 2000-120504 (JP 2000-120504 A) (p. 3 and FIG. 1), for example). In JP 2007-255361 A (pp. 5 to 6 and FIG. 1), when internal pressure in the fuel delivery pipe is added, high stress concentration is generated at a connecting portion where the fuel delivery pipe is connected to a socket provided near a center portion of the fuel delivery pipe, so the center portion of the fuel delivery pipe is reinforced with ribs to prevent an absorbing wall surface thereof from being damaged.
In JP 2000-120504 A (p. 3 and FIG. 1), a fuel delivery pipe is prevented from becoming axially offset from an injector due to a difference in thermal expansion caused by a temperature difference between the fuel delivery pipe and a cylinder head, by splitting up the fuel delivery pipe into sections and flexibly connecting the sections together. As a result, the sealing characteristic of a rubber O-ring at a portion where the injector and the fuel delivery pipe are connected is maintained.
A difference in material between the cylinder head and the fuel delivery pipe, or a temperature difference between the two, may result in a different degree of expansion between the two. For example, if the cylinder head is made of aluminum alloy and the fuel delivery pipe is made of iron alloy, the coefficient of linear expansion of the aluminum alloy is greater than the coefficient of linear expansion of the iron alloy, so the fuel delivery pipe receives force from the cylinder head that elongates the fuel delivery pipe when the internal combustion engine rises in temperature due to the internal combustion engine being operated. Conversely, when the temperature of the internal combustion engine is low, the fuel delivery pipe receives force from the cylinder head that shortens the fuel delivery pipe.
Even if the materials of the cylinder head and the fuel delivery pipe are the same, a temperature difference between the cylinder head and the fuel delivery pipe will similarly result in the fuel delivery pipe receiving forces from the cylinder head that cause it to become elongated and shortened.
When the fuel delivery pipe becomes deformed in this way, a sealing characteristic between the fuel injection valve and the fuel delivery pipe may decrease due to the entire fuel delivery pipe rebounding, or stress may concentrate at the fastening portion of the cylinder head and the fuel delivery pipe, which may cause the durability to decrease.
With the structure described in JP 2007-255361 A (pp. 5 to 6 and FIG. 1), the issue is deformation caused by the internal pressure of the fuel delivery pipe itself, so there is no measure against deformation caused by a difference in the coefficient of linear expansion between the fuel delivery pipe and the cylinder head. With the structure described in JP 2000-120504 A (p. 3 and FIG. 1), offset between the fuel delivery pipe and the cylinder head is reduced by reducing the difference in the thermal expansion at each portion by splitting up the fuel delivery pipe. However, because the fuel delivery pipe has been split up in this way, the strength of the fuel delivery pipe itself is reduced.